There are many different servers which can provide Signal K data. The first sections of this document explain the installation of Signal K node server for node.js, an implementation of Signal K server available on multiple platforms.

This is the platform which is probably the best supported, please read a comprehensive list of instructions here:

https://github.com/SignalK/signalk-server-node/blob/master/raspberry_pi_installation.md

It gives not only information about the installation, but also for the configuration and is therefore good reading even if you do not own a Rasperry Pi.

The generic installation instruction in the server's repository are less detailed than for Raspberry Pi, but enough to get the server started:

https://github.com/SignalK/signalk-server-node#installation

You fill find from the main page of this wiki section for Signal K a page which gives you information how to configure the server for the usage with OpenCPN.